Deep brain stimulation (DBS) represents a therapy that may be used to treat and relieve various neurological disorders, such as Parkinson's disease, tremors, dystonia, psychiatric illness, and the like. In general, DBS may include electrically stimulating certain areas of the brain to alter or otherwise affect motor function and behavior to alleviate the effects of a neurological disorder. The motor and behavioral effects of brain stimulation typically depend on a location of a stimulating electrode within the brain. Accordingly, DBS generally requires accurate, precise, and safe targeting of brain structure. In order to locate and target specific areas of the brain, surgeons typically rely on a preoperative plan that includes a pathway to the specific target within the brain.
For example, a desired target for treating Parkinson's disease is located in the dorsolateral portion of the sub-thalamic nucleus (STN) of the brain (the entire STN is approximately 3-4 mm in diameter). Other targets such as the globus pallidus or targets in the thalamus are typically no greater than 4-5 mm in diameter. For such small targets, deviation from the target site by as little as 1 mm may not just reduce the effectiveness of treatment, but may also induce undesired side effects such as weakness, altered sensation, slurred speech, double vision, and/or the like. Thus, DBS typically requires accurate surgical planning and targeting of specific locations within the brain.
In general, a DBS process includes positioning a stereotactic frame on a head of a patient, surgical planning, and placing one or more leads or probes within the brain. A DBS process may start with acquiring an image of the brain. For example, a magnetic resonance imaging (MRI) system may acquire an MRI image of the brain. Next, a stereotactic frame is mounted to the skull of the patient. An additional image, such as acquired with a computed tomography (CT) system, is acquired of the patient with the stereotactic frame secured to the skull. A computer then merges the MRI and CT images. A surgeon then uses the merged images to plan the DBS procedure.
During the planning stage, a target area may be identified and located within the merged images. For example, a surgeon may locate the globus pallidus internus or sub thalamic nucleus. The surgeon may then determine implant coordinates of the stereotactic frame that will direct a microelectrode toward the target area.
After the surgical plan including a path to the target area is determined, a burr hole is formed in the skull of the patient. For example, a surgical drill may be used in conjunction with the stereotactic frame to drill a hole through the skull, thereby exposing the brain cortex. The drill may then be removed from the stereotactic frame.
A driving mechanism in conjunction with the stereotactic frame may then be used to move a microelectrode recording probe through a guide tube that passes into the burr hole and into the brain. The microelectrode recording probe is advanced through the guide tube and into the brain while recording neuronal activity during advancement into the brain towards the target area.
Neurons in the target area in the brain typically generate action potentials in known bursting patterns at different frequencies depending upon the respective location. The surgeon may be familiar with such patterns. Thus, the recordings from the microelectrode recording probe may be used to assist the surgeon in determining the correct path to the target area and in determining whether the target area has been reached. For example, neuronal activity recorded by the microelectrode recording probe may be displayed as waveforms on a monitor. Alternatively, or additionally, the acquired neuronal activity may be amplified and output to a speaker. The generated signal, whether shown as waveforms on the display or output through the speaker, allows the surgeon to determine whether or not the microelectrode is on the correct path to the target area. If the surgeon recognizes the generated signal as consistent with a path toward the target area, the surgeon continues to advance the microelectrode on the pre-planned path. If, however, the surgeon determines that the output signal recorded by the microelectrode recording probe is inconsistent with the path toward the target area, the surgeon may discontinue advancement of the microelectrode recording probe, and advance another microelectrode on a different path toward the target area.
Assuming that the microelectrode recording probe is on the correct path, the surgeon may continue to advance the microelectrode recording probe toward the target area until it is a short distance, such as 1-5 mm, from the target area. The surgeon then removes the microelectrode recording probe from the guide tube, and inserts a stimulation lead into the guide tube. The stimulation lead is then advanced into the target area so that electrical pulses from an electrode of the stimulation lead may be directed into the target area.
The surgical plan including the path to the target area may not, however, be accurate. For example, during the drilling of the burr hole, the brain may shift due to pressure changes when air passes into an interior of the skull. Further, the stereotactic frame may also slightly shift, such as if the patient's head moves within the stereotactic frame. Moreover, image superposition and registration algorithm errors may occur. As such, the path to the target area as determined during the surgical planning stage may deviate from a correct path to the target area.
Such errors may cause the target area to be missed, and/or may cause the surgeon to re-advance the microelectrode recording probe in a different and parallel path to the original path determined by the surgical plan. The surgeon may test multiple parallel paths to the target area. For example, the surgeon may test 1-4 additional paths toward the target area with the microelectrode recording probe until a correct path to the target area is found. However, each time a microelectrode recording probe is advanced into the brain, a risk of brain hemorrhage increases.
Accordingly, current systems and methods that are used to plan and test surgical paths to a target area within a brain may not be entirely accurate, and may pose risks of brain hemorrhage, damage, and the like.